1. Technical Field of the Invention
The present invention relates to a dinaphthyl ethylene derivative, a process for preparing it, a film prepared from it useful in the manufacture of an organic light emitting device (abbreviated as OLED hereinbelow), an OLED including the film, and the use of the dinaphthyl ethylene derivative in the manufacture of an OLED.
2. Description of the Related Art
OLED came into being in the 1960s. In 1963, P. Pone et al first observed the light emitting phenomenon of anthracene crystal. However, its driving voltage was as high as 400 V, and for that reason this phenomenon failed to attract sufficient human attention. In 1987, an amorphous film diode, an organic light emitting device, was made of Alq3 and HTM-2 by sublimation coating by C. W. Tang et al in Kodak., and its driving voltage was as low as less than 20 V. From then on, OLED began to attract much attention the world wide (see U.S. Pat. No. 4,356,429). OLED features high brightness, wide angle, quick electric response, low driving voltage, low energy consumption, full color, high contrast, light weight, easy making and so on. Thus, it is widely used as panel luminance diode, for example, in flat panel display and light pan.
OLED comprises two electrodes and at least one organic film disposed between them. The organic film is made from an electroluminescent compound. Typically, electroluminescent compound with a structure of D-π-X (D means Donor Group) contributes to form an OLED having a high efficiency of fluorescence. Additionally, the emission wavelength of the OLED depends on X: the compound wherein X represents a strong donor group, such as a diaminoanthracene derivative synthesized by Cheng C. H. (see Chem. Mater., 2002, 14:3958), forms an OLED usually emitting green light; the substance wherein X represents a weak donor group, such as a coumarin derivative synthesized by Chen C. T. (see Org. lett., 2003, 5: 1261), a anthracyl arylamine synthesized by Lin J. T. (see Chem. Mater., 2002,14:3860), or a carbazolyl oxadiazole synthesized by Huang C. G. (see Chem. Commun., 2003, 2708), forms an OLED emitting blue light; the substance wherein X represents a strong acceptor group, such as a NPAFN derivatives (see Chem. Commun., 2003, 2632), forms an OLED emitting red light. On the other hand, the π bridge is also important. A too large π bridge renders the emission wavelength of the resulting OLED longer, a phenomenon which in turn negatively affects color purity of the OLED. Conversely, a too small π bridge reduces the current efficiency of the OLED. For instance, an electroluminescent compound with a diphenyl ethylene group forms an OLED showing bad performance in terms of current efficiency and life span (see CN1388800A).